1. Technical Field
This invention relates to a method and device for determining the distance and position of stationary and moving objects, for example within an area to be monitored in connection with, for instance swing doors.
2. Description of the Prior Art
It is known to use sensors for detecting objects, such as people, in close vicinity to, for example swing doors which open automatically. One common sensor is a pressure-sensitive mat placed in front of the door where the form and size on the mat is adapted to current rules and criteria. The disadvantage with such mats is that they quickly become worn out, they are expensive since they must often be recessed on the ground level and that they are sensitive to sharp objects such as heels and stones. Another known sensor is based on the capacitive function but the disadvantage with this sensor is that it is sensitive to disturbances from the temperature, dampness and so on. In addition, it is difficult with this sensor to distinguish between stationary objects that are close to each other. For moving objects, it is known to use sensors based on microwave and the Doppler effect technology. Using passive infra-red technology is also known but the disadvantage of this is the difficulty in detecting objects which have the same temperature as their surroundings. Finally, it is also known to use active infra-red technology in sensors but these known devices often have the disadvantage of the object's size and properties of reflection greatly affecting the distance of detection and sensitivity. For sensors of the above types, it is necessary that they fulfill certain stipulated requirements, for example the requirements on the size and form of the security area, the capacity to be able to distinguish between several objects in the area, response time, noise tolerance and so on.
The method according to this invention provides a solution to the above given problems.